Among the more challenging illumination tasks for solid-state lighting is forward lighting meeting predefined criteria, such as forward lighting for vehicles, utilizing non-thermal light sources, e.g., light-emitting diodes (LEDs). The lifetime of LEDs in the vibration environment of a ground vehicle is far greater than that of conventional incandescent sources. Some recently developed white LEDs are surpassing the significant 100-lumen luminosity threshold, marking the feasibility of fulfilling that most difficult of all forward vehicle lighting tasks, automotive-headlight intensity standards. Peak intensities in the tens of thousands of candela, however, can not be achieved with LEDs alone.
Beyond efficiency, moreover, automotive design pressures for highly compact forward-lighting systems pose severe tradeoffs of device size against attainment of sharp intensity cutoffs required to minimize glare to other vehicles. Prior LED optics employ unacceptable device size when compared to competing incandescent-source designs such as projector lamps.